While there is not much one can say about single-use objects like mounting rings, there were a couple of points which struck me when I received and examined them.
Firstly, they are quite sturdy, and could be used for fairly weighty equipment, but light in weight.
Secondly, they come with a flattened part of the ring so that they could be mounted directly onto, say, a telescope mounting bar. If this isn't to your liking, and you would prefer a "nice" round ring assembly, Prima Luce Lab have thoughtfully provided fill-in sections with screws.
Thirdly, the 'scope mounting screws are each tipped with a nylon pad that doesn't dent or scratch (unless you are over enthusiastic in tightening them). They seem to hold objects quite well without undue tightening.
Overall, I am impressed with the quality, design and workmanship of these rings. I am using mine to hold a long image train firmly in place while my 'scope tracks the sky. The rings clamp onto my imaging camera and the arrangement is rock solid, without any sign of damage to the camera's casing. I am well pleased with my purchase!